Prepare line — to catch this? (4)
I believe the answer is:
dory
'catch this?' is the definition.
(dory is a type of fish)
'prepare line' is the wordplay.
'prepare' becomes 'do' (I've seen this in other clues).
'line' becomes 'ry' (abbreviation for railway).
'do'+'ry'='DORY'
'to' is the link.
(Other definitions for dory that I've seen before include "Fish and flat-bottomed boat" , "Golden-yellow fish" , "Fish for a small boat" , "Fish of mackerel family" , "Marine fish; rhymes with fable" .)